Populations east of the Apalachicola River Basin and Appalachian Mountains have been diverging from western populations (the form mavortium) for approximately 1 million years. Collectively, eastern populations might constitute a distinct species (Church et al. 2003).

Justification:
Listed as Least Concern in view of its wide distribution, tolerance of a broad range of habitats, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

This species can be found throughout much of the USA, southern Canada to northern Mexico in the Sierra Madre Occidental. It is absent from most of the Great Basin, New England, and the Appalachian mountains. From sea level to around 3,660m asl in the Rocky mountains. Introduced populations occur in central California [not mapped here], where they hybridise with A. californiense (Riley et al., 2003); in the western U.S. populations are sometimes moved in association with the fish bait industry. In Mexico, the species apparently has a limited distribution in the northwest, where its interactions with A. velasci require additional investigation.

This is one of the most abundant Ambystoma species. The total adult population size is unknown but surely exceeds 1,000,000. Tiger salamanders occur throughout their historical range in the Rocky Mountains and Great Plains of Colorado and adjacent states. They remain easy to find and locally abundant in suitable habitat statewide. Ponds often contain up to several thousand larvae. Recent surveys found no evidence of significant declines in distribution or abundance (Corn, Stoltzberg, and Bury 1989; Hammerson 1989a, 1992; Corn, Jennings, and Muths 1997). In the Rocky Mountains, a local decline in numbers over several years, reported by Harte and Hoffman (1989), turned out to be a temporary fluctuation from which the population subsequently recovered (Wissinger and Whiteman 1992). Hovingh (1986) reported that tiger salamanders remain quite common in aquatic systems in glaciated portions of the Uinta Mountains in northeastern Utah. The widespread creation of small, fishless artificial bodies of water has provided much suitable habitat where previously there were little, and these salamanders have been quick to colonize it (Norris 1973; pers. obs.). Populations east of the Appalachians are highly patchy in distribution with several local extirpations having been documented over the past 20 years. Remaining eastern populations are small in size and several are in decline (Church 2003, Semlitsch et al. 1996, Zappalorti 1994). In Mexico this species is generally not uncommon.

It can be found in virtually any habitat, providing there is a terrestrial substrate suitable for burrowing and a body of water nearby suitable for breeding. Terrestrial adults usually are underground, in self-made burrows or in those made by rodents, shrews, or other animals. In New York, adults on land used wooded areas and avoided grassy areas (Madison and Farrand 1998). At high elevations in the Rocky Mountains, metamorphosed adults commonly occur in ponds throughout the summer. Eggs are attached to submerged objects or pond bottom. Breeds in a wide range of environments, ranging from clear mountain ponds to temporary, manure-polluted pools in the lowlands. Always breeds in sites where predatory fishes are absent. In the mountains of western Colorado, associated with ponds that have silty bottoms, low alkalinity, and no fishes (Geraghty and Willey 1992). In the southeastern U.S., requires relatively flatwoods ponds that do not contain fishes.

In Mexico it has been observed that in some localities this species can resist conditions of pollution and other kinds of alteration of the environment. Many mountain lakes formerly inhabited by tiger salamanders now have few or none of these amphibians due to the stocking of trout, which easily consume and deplete the larval populations (e.g., Blair 1951; pers. obs.). Geraghty and Willey (1992) found that fish absence was the most important factor influencing tiger salamander presence in Gunnison County and vicinity, and Corn, Jennings, and Muths (1997) reported that trout and tiger salamanders rarely occur together in Rocky Mountain National Park. Trout and tiger salamanders do occasionally coexist in some lakes (Dartt 1879; Blair 1951), but only where vegetated shallows provide habitat not easily accessible to the fishes. Some have suggested that breeding-pond acidification related to atmospheric pollution might cause periodic failure of tiger salamander reproduction in the mountains of Colorado (Harte and Hoffman 1989, 1994). Low pH, even if not fatal to salamander larvae, might result in reduced growth rates and ultimately could diminish salamander populations through decreased survival or feeding success (Kiesecker 1996). However, recent water chemistry data, together with information on acid tolerances of salamander larvae, suggest that eggs and embryos in the wild do not experience harmful levels of acidification (Corn, Stoltzenburg, and Bury 1989; Corn and Vertucci 1992; Wissinger and Whiteman 1992; Vertucci and Corn 1994). Under certain conditions, larval populations might be vulnerable to bacterial infections associated with livestock grazing. In the mountains of Utah, Worthylake and Hovingh (1989) observed recurrent mass mortality of larvae associated a bacterial infection and suggested that increased nitrogen levels due in part to sheep grazing might have been involved. Bryant (1995) observed a mass mortality event in the summer of 1993 that appeared to be associated with an opportunistically pathogenic bacterium. In Arizona, similar die-offs, apparently associated with bacterial pathogens, have been reported (Pfennig, Loeb, and Collins 1991). Cannibal morphs seemed particularly vulnerable, probably due to their feeding on diseased larvae. Again, fecal contamination of ponds by introduced livestock was suggested as a possible cause of the fatal outbreaks. In contrast to these reports, larvae sometimes do thrive in large numbers in manure-laden ponds in Colorado (Hammerson 1999). Nevertheless, die-offs of larvae, apparently associated with pathogenic bacteria, have been observed in Colorado (Hammerson 1999). Populations in the southeastern USA have been detrimentally affected by deforestation and loss of wetland habitats and appear to be declining (Petranka 1998). Population viability analyses of populations in the eastern USA have shown that demographically isolated populations are highly susceptible to extinction, particularly under conditions of high weather variability (Church 2003).This species is sometimes found in the international pet trade but at levels that do not currently constitute a major threat.

Needed measures include basic habitat protection and policies/regulations that discourage/prohibit the introduction of predatory fishes into habitats where they are not native. Further research on phylogeographic patterns and taxonomic status of major population segments is needed. This species is protected under the category Pr (Special protection) by the Government of Mexico.